Dielectric structures having embedded gap filling RIE etch stop polymeric materials of high thermal stability

ABSTRACT

Structures containing a dielectric material having a polymeric reactive ion etch barrier embedded therein. The preferred dielectric materials are polymers, preferably polyimide materials. The RIE etch barrier is a copolymer having an aromatic component having high thermal stability and having a cross-linking component selected from metallacyclobutane, metallabutene and vinyl groups. The etch barrier is deposited as a solvent free liquid which can fill gaps between the dielectric material and electrical conductors embedded therein. The liquid polymer is cured to a solid insoluble state. The structures with electrical conductors embedded therein are useful for electronic applications.

This is a continuation of application Ser. No. 07/693,976, filed Apr.29, 1991 now abandoned, which is a continuation of application Ser. No.07/366,089, filed Jun. 13, 1989, U.S. Pat. No. 5,141,817.

FIELD OF THE INVENTION

This invention relates to dielectric structures having imbedded thereina polymeric material which is resistant to reactive ion etching. Inparticular, this invention relates to polyimide structures forelectronic applications. More particularly, this invention relates topolyimide structures, for electronic applications, having electricalconductors embedded therein and a polymeric layer which is resistant toreactive ion etching, which has high thermal stability and which iscapable of filling gaps between the electrical conductors and thepolyimide structure.

BACKGROUND OF THE INVENTION

In electronic applications multi-level polymer structures are beingincreasingly used, for example, as the top metallization structures ofsemiconductor chips, semiconductor chip packaging substrates and asindependent structures for electrically interconnecting a semiconductorchip to a semiconductor chip substrate. These multi-level polymerstructures are used since they can be fabricated independently of thestructure on which they are disposed. For example, a semiconductor chip,or a semiconductor chip packaging substrate can be fabricated to a levelhaving a predetermined terminal electrical conductor pattern. Amulti-level polymer structure can be fabricated having on a first sidean electrical conductor pattern corresponding to the terminal electricalconductor pattern of the chip or substrate. On a second side of themulti-level polymer structure a variety of terminal or input/outputconductor patterns can be fabricated. An easily implemented andinexpensive personalization of the semiconductor chip or semiconductorchip packaging substrate is provided by disposing the first side of themulti-level polymer structure onto the chip or substrate.

Semiconductor chip packaging substrates are typically made from ceramicmaterials having multi-level conductor patterns therein. Electricalconducts in the upper levels are used to electrically interconnect thesubstrate to the input/output terminals of the semiconductor chipmounted thereon. Therefore, the upper levels require a denser electricalconductor pattern than other levels in the substrate. Patterns of finerdimensions can be fabricated in polymer materials than in the ceramicmaterials. Therefore, the use of multi-level conductor polymerstructures permits the terminal metallization layers of a semiconductorchip packaging substrate to have electrical conductors which havesmaller dimensions and which are more closely spaced than is capable ofbeing fabricated in the ceramic material of a ceramic semiconductor chipsubstrate.

A multi-level polymer structure is typically fabricated by providing afirst polymer layer using standard photolithography techniques forming apattern of through-holes therein which are filled with an electricallyconducting material. A second polymer layer is deposited thereover. Aresist like material is deposited onto the second polymer layer. Theresist like material is patterned and developed exposing regions of thesecond polymer layer. The exposed polymer regions can be etched by achemical etchant or a dry etchant, such as, as a reactive ion (RIE) orplasma etchant. For the purpose of this application RIE and plasmaetching are synonymous. RIE etching is the preferred etchant since itprovides straighter sidewalls to the pattern etched in the polymer layerand thereby forms a pattern having smaller dimensions. The RIE etchesdown through the second polymer layer and reaches the top surface of thefirst polymer layer. The RIE etching can be timed in order to stop it atthe appropriate depth. Timing the RIE etch results in a variable depthof the etched pattern. The variation in the depth is determined by theaccuracy of the timing of the etching as well as statistical variationsin the RIE etch parameters. The variation in the etched depth can beeliminated if an RIE etch barrier is provided between the first andsecond polymer layer. As a pattern is RIE etched in the second polymerlayer, the RIE etching stops at the etch barrier, thereby the etcheddepth is accurately controlled.

The inventions herein are not limited to RIE etch barriers embeddedwithin polymer materials but is generally applicable to such barriersembedded in a dielectric material.

It is an object of this invention to provide a dielectric body having anRIE etch barrier embedded therein.

Multi-level polymer structures used in electronic applications arecycled up to relatively high temperatures, for example, in excess of400° C. Therefore, RIE etch barrier disposed within a multi-levelpolymer structure should have high thermal stability.

It is another object of this invention to provide a polymer body havingan RIE etch barrier embedded therein.

It is another object of this invention to provide a polymer body havingan RIE etch barrier embedded therein which is useful for electronicapplications.

It is another object of this invention to provide a polymer body with anRIE etch barrier embedded therein which has high thermal stability.

When an electrical conducting material is deposited into a patternetched in a dielectric layer, typically there are spaces between thesidewall of the pattern in the dielectric material and the electricalconductor formed therein. Such spaces provide regions wherecontaminants, for example, created during the processing of thesubstrate, can accumulate. Contaminants such as ionic contaminants cancreate electrical short circuits between electrically conducting linesand can result in corrosion of the electrically conducting lines whichcan result in electrical opens. It is desirable to fill these spaces orgaps to avoid these undesirable effects.

The RIE etch barrier according to the present invention is deposited asa liquid polymer which has a viscosity sufficient to permit the polymerto flow into into the gaps between the electrical conductors and theetched pattern in the dielectric material. The liquid polymer isthereafter cured to cross-link the polymer to a solid state.

It is an object of this invention to provide a polymeric material whichfills the gaps between the electrical conductors and the dielectric bodywithin which it is embedded.

Polymeric materials according to the present invention whichsimultaneously act as a RIE etch barrier and are capable of fillingthese gaps are formed from a copolymer, one unit of which has hightemperature stability and at least one other unit of which is capable ofcross-linking the polymer.

It is another object of this invention to provide a polymeric materialhaving a high thermally stable component and a component permittingcross-linking.

RIE etching of substrates for electronic applications frequently useoxygen containing RIE etches. Prior art materials which an artisan mightsuspect would provide a high resistance to an oxygen RIE or plasma etchsuffer from several inadequacies. In the liquid state they have highviscosity mitigating against their ability to fill the gaps, they havelow resistance to the oxygen plasma or they have a low thermal stabilityprecluding their use in a high temperature cycling environment such asrequired as an intermediate layer in a dielectric structure forelectronic applications. The RIE etch barrier materials according to thepresent invention surmount these problems by having a low viscosity andbeing free of solvents which reduces the problems of shrinkage on curingand by having a high etch resistance with respect to the dielectricbody.

SUMMARY OF THE INVENTION

In its broadest aspect this invention is a dielectric body havingembedded therein polymer body which is a barrier to reactive ionetching.

In a particular aspect of the present invention, the polymer etchbarrier body is a cross-linked form of a copolymer containing silicon,germanium or transition metal, containing an aromatic constituent havinghigh thermal stability and containing a cross-linking constituentselected from a cyclobutane radical and a vinyl radical.

In a more particular aspect of the present invention, the aromaticconstituent having high thermal stability is selected from the group ofsubstituted or unsubstituted naphthalene, anthracene, adamantiveradicals, ferreceric and carborane radicals.

In a more particular aspect of the present invention the polymer body isa polyimide body.

In another more particular aspect of the present invention the polymerbody has embedded therein electrical conductors.

In another more particular aspect of the present invention, the polymerbody has at least one cavity in the dielectric body extending to thereactive ion etched barrier body.

In another more particular aspect of the present invention, the cavityis filled with an electrical conductor.

In another more particular aspect of the present invention, the RIE etchbarrier material fills gaps between the electrical conductor thesidewall of the opening in the dielectric body.

In another more particular aspect of the present invention, thedielectric body having electrical conductors embedded therein is asubstrate on which an electronic device is electrically mounted.

In another more particular aspect of the present invention, the polymerbody having electrical conductors embedded therein is the top surfacemetallization of an electronic device.

In another more particular aspect of the present invention, thecopolymer has structural formula: ##STR1## wherein Q is selected fromthe group consisting of groups having structural formula: ##STR2## whereR is a divalent aromatic radical; wherein R¹ is selected from the groupconsisting of H, a monovalent hydrocarbon radicals and a silyl radicalhaving structural formula: ##STR3## wherein each R² is selected from thegroup consisting of H and monovalent vinyl and alyl radicals preferablyalkyl, alkenyl and aryl radicals;

wherein each R⁴ is selected from the group consisting of H, a monovalenthydrocarbon radical and a silicon containing radical having structuralformula: ##STR4## wherein for the cyclobutane groups Q containingadjacent M atoms, R⁴ is preferably an organic radical such as methyl orlarger than methyl;

wherein each R⁵ is selected from the group consisting of hydrogen, analkyl radical and an aryl radical;

wherein each R⁶ is selected from the group consisting of monovalenthydrocarbon radicals, preferably alkyl and alkenyl radicals;

wherein R⁹ is selected from the group consisting of monovalenthydrocarbon radicals;

wherein R¹⁰ is selected from the group consisting of alkenyl radicals;

wherein Z is selected from the group consisting of aromatic radicals,preferably being phenylene, naphthalene and anthracene wherein Z forms asix member carbon ring with the two R⁴ to which is bonded;

wherein each M is selected from the group consisting of Si and Ge;

wherein P has a value such that said compound has a molecular weightfrom about 1,000 to about 30,000;

wherein m is at least 1; and

wherein n is greater than or equal to 0.

These and other objects, features and advantages will be apparent fromthe following more particular description of the preferred embodimentsand the figures appended thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a dielectric layer with through-holes therein.

FIG. 2 shows electrically conductive layer disposed over the structureof FIG. 1.

FIG. 3 shows the electronically conductive layer of FIG. 2 etch back tothe top surface of the dielectric layer.

FIG. 4 shows the structure of FIG. 3 with a layer of material forming anRIE etch barrier according to the present invention.

FIG. 5 is the structure of FIG. 4 with a dielectric layer disposed ontothe RIE etch barrier of FIG. 4.

FIG. 6 shows selective removal of the dielectric of the seconddielectric layer of FIG. 5.

FIG. 7 shows the RIE etch barrier removed at the bottom of the seconddielectric layer where the second dielectric has been removed.

FIG. 8 shows an electrically conductive layer disposed over thestructure of FIG. 7.

FIG. 9 shows the electrically conductive metal layer of the structure ofFIG. 8 etched back to the top surface of the second dielectric layer.

FIG. 10 is an expanded view of one of the electrical conductors in thestructure of FIG. 3 showing the polymeric etch barrier material fillingin gaps between the electrical conductor and the first dielectric layer.

FIG. 11 is a plot of a thermogravimetric analysis of an RIE etch barrierpolymer of the present invention.

FIG. 12 is a plot of the etch rate of the polymer of FIG. 11

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 to FIG. 9 schematically show a process to fabricate a structureaccording to the present invention.

In FIG. 1 dielectric layer 2 has through-holes 4 fabricated therein. Thethrough-holes can be fabricated by methods commonly used in the art, forexample, wet etching, dry etching, punching and drilling and the like.When wet or dry etching is used to fabricate the through-holes, aresist-like material is disposed on one surface of the dielectric layer2. The resist-like layer is typically a photoresist, for example, AZtype photoresist manufactured by Shipley. The photoresist is exposedthrough a mask to electromagnetic radiation, for example, light and theexposed patterns on thereafter developed. The exposed regions of thedielectric are thereafter wet or dry etched to etch the through-holes 4in the dielectric layer 2.

As shown in FIG. 2 an electrically conducting layer 6 is deposited oversurface 8 of the patterned dielectric 2 of FIG. 1.

As shown in FIG. 3 surface 10 of electrically conducting layer 6 isetched back, by methods commonly known in the art, to surface 8 of thedielectric layer 2 leaving through-holes 4 filled with electricallyconducting material 10 to form electrically conducting vias 12.

As shown in FIG. 4 RIE etch barrier layer 14 is disposed on surface 8 ofpolymer layer 2.

As shown in FIG. 5 a second dielectric layer 16 is disposed onto RIEetch layer 14.

By methods commonly known in the art, a resist-like material is disposedonto surface 18 of dielectric layer 16. The resist-like material istypically a photoresist which is exposed to electromagnetic radiation,for example, visible light, to form a pattern in the photoresist. Thepattern is developed and removed leaving a photoresist mask on surface18. The exposed regions of dielectric layer 16 are then exposed to anRIE etch or a plasma etch which attacks the exposed regions ofdielectric layer 16 etching through dielectric layer 16 down to the RIEetch barrier 14 as shown in FIG. 6 forming pattern 20 in dielectriclayer 16. For the purpose of this application RIE etch and plasma etchare synonymous. Exposed regions 22 of the RIE etch barrier 14 areremoved as will be described hereinbelow. The resulting structure shownin FIG. 7 has a pattern 20' through dielectric layer 16 and etch barrier14 exposing surface 22 of electrically conducting pattern 12 indielectric 2.

As shown in FIG. 8 a second electrically conducting layer 24 isdeposited over surface 26 of the structure of FIG. 7. Electricallyconducting layer 24 can be deposited by any means commonly known in theart such as sputter deposition, chemical vapor deposition,electroplating, electroless-plating and the like. The electricallyconducting layer 24 is etched back to surface 26 of dielectric layer 16resulting in the structure shown in FIG. 9.

FIG. 9 shows pattern 20' through dielectric layer 16 and RIE etchbarrier 14 filled with electrically conducting material 28 which are inelectrical contact with electrically conducting material 12 inthrough-holes 4 in dielectric layer 2.

It will be recognized by those of skill in the art that a structurehaving any number of dielectric and electrically conductive layers canbe fabricated by repeating the steps of FIGS. 1-9. The fabrication ofthe structure of FIG. 9 has been described in terms of formingdielectric layer having electrically conducting vias and anotherdielectric layer having conductors. Any number of layers havingelectrically conductive vias or electrical conductors or any combinationthereof can be fabricated by the method described herein.

The methods and structures described with reference to FIG. 1 to FIG. 9are exemplary only and not limiting.

Dielectric materials for layers 2 and 16 of the structure of FIG. 9 canbe ceramics and polymers. The preferred dielectric materials arepolymers. The most preferred dielectric material is a polyimidematerial. The electrically conducting material used to form electricalconductors 12 and electrical conductors 28 can be any electricallyconducting material. The preferred electrically conducting materials aremetals The most preferred electrically conducting materials are copper,aluminum, molybdenum, chromium, gold, silver and alloys thereof. The RIEetch used to fabricate patterns in the dielectric layers are preferablyoxygen containing. The most preferred RIE or plasma etch is O₂ and O₂/CF₄. Dielectric layers in the structure of FIG. 9 can have anythickness, the preferred thickness is from about 1 micron to about 10microns. The RIE etch barrier layer 14 can have any thickness, thepreferred thickness is from about 0.2 microns to about 1 micron.

The RIE etch barrier material 14 of FIG. 9 is a copolymer containing aunit having high thermal stability and a unit capable of cross-linkingwith other molecules of the copolymer. The RIE etch barrier layer 14 isdeposited onto surface 8 of FIG. 4 as a liquid copolymer which is thereafter cured to cross-link the polymer to form the RIE etch barrier layer14. The liquid co-polymer has a molecular weight between about 1000 toabout 30,000, this provides a sufficiently low viscosity so that theliquid polymer can flow into gaps 30 shown in FIG. 10 between electricalconductors such as 12 and sidewall 32 of through-hole 4 of dielectriclayer 2.

It is desirable to fill in gaps between the electrical conductors andthe dielectric layer within which it is embedded since gaps provideregions which can trap contaminants within the structure of FIG. 10.These contaminants can be chemicals used during the processing of thestructure of FIG. 10 or residues of the RIE etching or photoresistpolymers used in the processing as well as other materials. Contaminantscan introduce ions which can result in electrical short circuits betweenotherwise electrically isolated electrical conductors or can provide asource of corrosion of the embedded electrical conductors.

According to one aspect of the present invention, a liquid copolymerprecursor of the RIE etch barrier 14 of FIG. 9 is formed by reacting adisilyl or digerma substituted compound having high thermal stabilityrepresented by the following structural formula: ##STR5## with acyclobutane having structural formula: ##STR6## wherein each M isselected from the group of silicon and germanium; wherein R is abivalent aromatic compound preferably selected from the group consistingof a substituted or unsubstituted phenyl radical, a substituted orunsubstituted naphthalene radical, a substituted or unsubstitutedanthracene radical, a substituted or unsubstituted adamantine radical, asubstituted or unsubstituted ferrocene radical, and a substituted orunsubstituted carborane radical, wherein the most preferred bivalentradical is an unsubstituted phenyl radical;

wherein R¹ is a monovalent radical selected from the group of hydrogen,alkyl aryl and alkenyl, R¹ is preferably hydrogen;

wherein each R² is a monovalent radicals each being selected from thegroup consisting of hydrogen, monovalent alkyl, aryl and alkenylradicals and a siloxy radicals, wherein R² is preferably methyl andwherein the siloxy radical has the following structural formula:##STR7## wherein each R⁵ is selected from the group consisting of analkyl radical, an aryl radical and an alkenyl radical;

wherein each R⁴ is selected from the group consisting of hydrogen, analkyl radical, an aryl radical, an alkenyl radical and a silyl radicalhaving structural formula: ##STR8## R⁴ is preferably an alkyl radical,most preferably a methyl radical; wherein Z is selected from the groupconsisting of aromatic radicals, preferably substrated and unsubstratedphenylene, naphthalene and anthracene, wherein Z forms a six memeberedcarbon ring with the two R⁴ to which it is bonded wherein Z can be, forexample --R¹⁵ C═R¹⁶ C--R⁷ C═R¹⁸ C-- wherein R¹⁵, R¹⁶, R¹⁷ and R¹⁸ areorganic radicals;

wherein R⁵ is a monovalent radical selected from aryl, alkyl and alkenylradicals;

wherein M is selected from the group consisting of silicon and germaniumatoms;

wherein X is an anionic leaving group selected from the group consistingof halide ions, most preferably chlorine ions.

In a solvent approximately equimolar amounts of the substituted aromaticcompound of equation 1 is mixed with the cyclobutane compound ofequation 2 with approximately twice the number of moles of a HClacceptor, e.g., pyridines, triethylamine and the substituted aminies, toresult in a copolymer having structural formula: ##STR9## wherein Y isone of the bivalent radicals of equation 2.

Typical solvents are tolyene, xylene, diglyme, amylacetate,tetrahydrofurane.

The value of t depends on the desired molecular weight. The molecularweight of the condensation product of equation 4 depends upon thereaction conditions and can be regulated to be in the range from about1,000 to about 30,000 liquid oligomers. It will be recognized by anartisan that molecular weight can be controlled by the type of HClaccepter, reaction time, type of solvent and concentration ofcomponents.

The structure of the oligomers (equation 4) contain the reactivemetallocyclobutane ring which can undergo thermal or catalyticpolymerization forming cross-linked insoluble products from thecondensation product of equation 4. In the preferred embodiment acatalyst is not used.

In the preferred embodiment the substituted aromatic compound ofequation 1 is a disilyl substituted compound, being most preferablybis(hydroxydimethylsilyl) benzene. A metallocyclobutane of equation 2preferably contains silicon, being most preferably,1,1-dichloro-1-silacyclobutane. The condensation product of equation 4formed from the most preferred compounds of equations 1 and 2 can bethermally cross-linked at a temperature from between about 170° C. toabout 210° C. in from about 15 to about 30 minutes. If1,1-dichloro-3,3-dimethyl-1,3-disilacyclobutane is used instead of1,1-dichloro-1-silacylcobutane to prepare an oligomer according toequation 4, the cross-linking temperature can be reduced to 80°-100° C.

The molecular weight of the product of equation 4 is adjusted to be inthe range from about 1,000 to about 30,000 liquid oligomers so that theliquid polymer will have a sufficiently low viscosity to fill the gapsbetween the electrical conductors and dielectric substrate within whichit is embedded.

The condensation product of equation 4 forming the liquid polymer isseparated from the solvents by commonly used techniques.

As shown in the following sequence of equations, heat H is supplied tothe liquid polymer of equation 4 resulting in the opening of themetallocyclobutane ring via a bipolar intermediate resulting in crosslinking of the material and possible grafting to the polymericsubstrate, for example polyimide, as shown in equation 6. ##STR10##

A catalyst is not necessary to open the cyclobutane ring. It is believedthat cross-linking occurs from the chemical interaction of the positiveend of the open ring on one molecule of equation 6 with the negative endof the open ring of another molecule of equation 6. Equation 7 shows thecross-linking with only two molecules being cross-linked. The three dotsoccurring in two locations in equation 7 indicates further cross-linkingwith molecules of equation 6. Polymerization chain termination of thebipolar intermediate of equation 6 can result in grafting of thecross-linked polymer of equation 7 to a substrate on which it isdeposited. In the preferred embodiment the substrate is a polymer, mostpreferably a polyimide. Polyimide materials contain an imidefunctionality which has a cyclic ring which can be opened upon theapplication of heat. As represented by equation 8, when the polymer ofequation 6 is deposited on a PMDA-ODA polyimide and heated to cross-linkthe polymer of equation 6, the imide ring of the polyimide opensresulting in the structure of equation 9 wherein the cross-linkedpolymer is grafted to a nitrogen atom in the open imide ring of thepolyimide material. About 210° C. is sufficient to open the PMDA-ODAimide ring.

The polyimide is not limited to PMDA-ODA (pyromelaicdianhydrideoxydianiline). The Encyclopedia of Chemical Technology, Third Edition inthe article entitled "Polyimides", Vol. 18, pp. 702-719, the teaching ofwhich is incorporated herein by reference, describes various polyimidematerials including homopolymers.

Enhanced adhesion of the RIE etch barrier to a polymer substrate can beachieved by treating the polymer substrate to a water vapor plasma priorto disposing the liquid polymer, which forms the RIE etch barrier,thereon. Details on using a water vapor plasma to promote the adhesionof a first and second polymer layer can be found in U.S. patentapplication Ser. No. 332,656 filed Apr. 3, 1989 entitled "Method forEnhancing the Adhesion of Polymer Surfaces by Water Vapor PlasmaTreatment" to Chou et al., now U.S. Pat. No. 5,019,210, the teaching ofwhich is incorporated herein by reference.

The degree of cross-linking can be regulated by regulating the amount ofthe cyclobutane groups in the oligomer of equation 5 by substituting thecyclobutance groups with some other difunctional nonreactive groups.

This can be accomplished, for example, by adding to a solvent a halideacceptor, k molecules of the compound of equation 1, p molecules of thecompound of equation 2 and n molecules of the compound having thefollowing structural formula: ##STR11## wherein M is as defined aboveand wherein R⁶ and R⁷ are selected from the group of alkyl and alkenylradicals. The product is the terpolymer shown in equation 11 wherein Yis one of the bivalent radicals of equation 2. ##STR12##

It will be apparent to an artisan that the ratio of k to p to m iscontrolled by concentration of the constituents used to fabricate thecompound of equation 11. For example, k=10, p=10 and m=1 when 10 molesof bis (hydroxydimethylsilyl) benzene, 10 moles of dimethyldichlorosiland 1 mole of 1,1-dichiro-1-silacyclobutane is reacted in a solventcontaining a pyridines as HCl acceptor.

The terminal OR¹ groups of equation 6 and 11 can be substituted bytriarylsilyl groups if an excess of the monofunctional monomer havingstructural formula: ##STR13## is used in the starting reaction mixtureto fabricate the structure of equation 5 and equation 11. M and X are asdefined above and each R⁸ is selected from the group of aryl and alkylradicals. The most preferred monofunctional monomer istrimethylchlorosilane.

The cross-linking constituent of polymer of equation 5 and equation 11is a metallocyclobutane ring. A vinyl containing compound can replace ametallocyclobutane as the cross-linking agent of equation 10 andequation 3. The vinyl compound has structural formula: ##STR14## whereinat least one of R⁹ and R¹⁰ is an alkenyl radical containing at least onecarbon carbon double bond, being most preferably an ethelene radical. Ifonly one of R⁹ or R¹⁰ contains a carbon carbon double bond, the othercan be an alkyl or aryl radical.

As shown in the following sequence of equations, in a solvent containinga halide acceptor, approximately equimolar amounts of the compound ofequation 13 is combined with the compound of equation 1. ##STR15##

The product of equation 14 corresponds to equation 5 with thecyclobutane ring replaced with the vinyl containing group of equation13, wherein constituents R, R¹, R², R⁹, R¹⁰ and M are definedhereinabove.

Equation 15 corresponds to equation 11 with the cyclobutane ringreplaced by the vinyl containing group of equation 13, whereinconstituents R, R¹, R², R⁶, R⁷, R⁹, R¹⁰, M, K, P, M and are deferredabove. ##STR16##

Cross-linking of the polymers of equation 14 and equation 15 generallywill require either a photo-initiator or a thermal initiator to open upthe carbon carbon double bond. An example of a radical photoinitiator isIRGACURE (manufactured by Ciba-Geigy) which is added up to 10% by weightof polymers of equation 14 and equation 15. The mixture of the polymerof equation 14 or equation 15 and the radical photo-initiator isirradiated with light for example, at frequency 248 nm when IRGACURE isused as the photo-initiator. Alternatively, a thermal radical initiatorjust requires heat to open the vinyl carbon carbon double bond. Examplesof thermal initiators are, AIBN (manufactured by Aldrich Chemical Co.)or azobisisobutyrolnitrile, which requires greater than about 60° C. topolymerize carbon-carbon double bonds.

The following equation 16 represents the cross-linked product ofequation 15 when R⁹ is ethylene radical and R¹⁰ is methyl radical. Inthe preferred embodiment the compound of equation 15 is a vinylcontaining silphenylenesiloxane oligomer. ##STR17##

Materials of the equations 5, 11, 14 and 15 can be used as RIE barrierlayers. When exposed to an an oxygen containing plasma the organicconstituents are oxidized into volatile compounds leaving and oxides ofthe M, e.g. silicon oxides, constituent which are not volatile. (Whenrequired, these materials can be removed by etching inflourine-containing plasmas). All of these materials have high thermaland thermo-oxidative stability. For example, in FIG. 11 is shown athermogravimetric analysis (TGA) of a disilylphenylene silacyclobutanecross-linked polymer of equation 7 wherein R¹ is hydrogen, wherein R² ismethyl, wherein R is a bivalent phenyl radical, and wherein R⁴ ismethyl, wherein M is Si and t has a value such that the polymer has amolecular weight of 5000. Axis 40 is percent weight. Axis 42 istemperature in degrees centigrade. Curve 44 is for heating the sample inan atmosphere of nitrogen and curve 46 is for heating the sample inatmospheric oxygen. For heating in nitrogen, there is no appreciablechange in the polymer until after the polymer is heated above about 500°C. For the sample heated in air there is no appreciable change in thepolymer until the sample is heated above about 400° C. For the compoundsdescribed herein as etch barriers there is generally no expectedappreciable change until heated above 350° C.

FIG. 12 shows the result of etching a sandwich structure. The polymerhaving the TGA data of FIG. 11 is sandwiched between two PMDA-ODApolyimide layers. The sandwich structure was baked at 360° C. to cureall the polyimide layers. In the preferred embodiments R, R¹, R², R⁴,R⁵, R⁶, R⁷, R⁹ and R¹⁰ are as defined as follows:

The polyimide layers were 2 microns each and the silylphenylene layerwas 0.6 microns. The etch is an O₂ /CF₄ (2% CF₄) plasma. FIG. 12 showsthe etch data with axis 48 being the etch rate in angstroms per minuteand axis 50 being the etched time in minutes. Curve 52 corresponds tothe etch as a function of time, curve 54 is a laser interferometermeasurement to determine the etch rate. The distance between two peaksof curve 54 is 2000 angstroms as shown in the figure. There is about a20:1 etch ratio between the polyimide represented by region 56 and theetch barrier represented by region 58.

In the preferred embodiments R, R¹, R², R⁴, R⁵, R⁶, R⁷, R⁹, and R¹⁰ aredefined as follows:

R is preferably phenylene, most preferably a bivalent phenyl radical;

R¹ is preferably H or lower alkyl having from 1 to 10 carbon atoms; mostpreferably H;

R² is preferably lower alkyl and alkenyl having from 1 to 10 carbonatoms, aryl having from 1 to 3 benzene rings and siloxy radicals, mostpreferably methyl;

R⁴ is preferably H, lower alkyl and alkenyl having from 1 to 10 carbonatoms, aryl having from 1 to 3 benzene rings and a silyl radical, mostpreferably methyl;

R⁵ is preferably H, lower alkyl and alkenyl having from 1 to 10 carbonatoms, and aryl having from 1 to 3 benzene rings; most preferablymethyl;

R⁶, R⁷ and R⁹ are preferably lower alkyl and alkenyl having from 1 to 10carbon atoms and aryl having from 1 to 3 benzene rings, most preferablymethyl;

R¹⁰ is preferably lower alkenyl having from 1 to 10 carbon atoms, mostpreferably ethylene.

EXAMPLES Example 1

22.6 gm p(bis-hydroxydimethylsilyl)benzene were dissolved in 200 mltoluene, 32 g pyridine were added and then 19.1 gm of1,1-dichloro-1-silacyclobutane were added to the solution at roomtemperature under stirring conditions. The reaction mixture was filteredafter 17 hours (at 20° C.) to remove the precipitate (Py.HCl salt) andthen poured into methanol (10% H₂ O). The bottom layer of thepolysilphenylene copolymer was separated, kept under vacuum (150 mm,100° C., for 2 hours) to remove all volatile compounds, filtered andused as an etch barrier. Molecular weight (GPC data was 2,2.10⁴)dispersivity, 2,0₀ the oligomer contains app. 28.6% Si, the etch rate inO₂ (CF₄) plasma was 60 Å/min at 200 m Torr. TGA data show that nodegradation occurs up to 400° C.

Example 2

Example 1 is repeated except that 1,3-dichloro-1,3dimethyl-1,3-disilacyclobutane is used instead of1,1-dichloro-1-silacyclobutane.

Example 3

Example 1 is repeated except that1,1-dichloro-3,3-dimthyl-1,3-disilacyclobutane is used instead of1,1-dichloro-1-silacyclobutane.

Example 4

Example 1 is repeated except that1,1-dichloro-2,3-benzo-1-silacyclobutene is used instead of1,1-dichloro-1-silacyclobutane.

Example 5

Example 1 is repeated except that1,1-dichloro-3-methyl-1-silacyclobutane is used instead of1,1-dichloro-1-silacyclobutane.

Example 6

Example 1 is repeated except that1,1-dichloro-2-phenyl-1-silacyclobutane is used instead of1,1-dichloro-1-silacyclobutane.

Example 7

Example 1 is repeated except that1,1-dichloro-3,3-diphenyl-1,2-disilacyclobutane is used instead of1,1-dichloro-1-silacyclobutane.

Example 8

Example 1 is repeated except that 1,1-dichloro-1-germacyclobutane isused instead of 1,1-dichloro-1-silacyclobutane.

Example 9

Example 1 is repeated except that1,1-dichloro-3,3-dimethyl-1-sila-3-germacyclobutane is used instead of1,1-dichloro-1-silacyclobutane.

Example 10

Example 1 is repeated except that a mixture of three comonomers,p(bis-hydroxy-dimethylsilylbenzene) (22.6 g), dimethyldichlorosilane(12.9 g) and 1,1-dichloro-1-silacyclobutane (1.41 g) was used incombination with pyridine (32 g).

Example 11

Example 10 was repeated except that triethylamine was used in stead ofpyridine. Reaction time was 60 minutes.

Example 12

Example 1 is repeated except that a mixture of four comonomers,p(bis-hydroxydimthylsilyl), benzene (27.6 g) , dimethyldichlorosilane(12.9 g), 1,1-dichloro-1-silacyclobutane (1.41 g) andtrimethylchlorosilane (molecular weight regulator) (1 g) was used.

Example 13

Example 1 is repeated except that diethyl ether was used as a solventwhich was removed at 50° C. (150 mm Hg vacuum, for 2 hours).

Example 14

The oligomer at example 1 was spin-coated on top of imidized polyimideDu Pont Pyrelene 5878. After baking at 170° C. for 60 minutes it forms across-linked product.

While the invention has been illustrated and described with respect topreferred embodiments, it is to be understood that the invention is notlimited to the precise constructions therein disclosed, and that theright is reserved to all changes and modifications coming within thescope of the invention as defined in the appended claims.

Having thus described our invention, what we claim as new and desire tosecure by Letters Patent is:
 1. A method for grafting a polymericcompound on a polymeric substrate comprising:providing said polymericcompound, said polymeric compound contains a metallacyclobutaneconstituent, said metallacyclobutane constituent contains at least onemember of the group consisting of Si and Ge atoms; thermallycross-linking said polymeric compound by opening said metallcyclobutanegroup; said polymeric compound being cross-linked through said openedmetallocyclobutane group; disposing said polymeric compound on asubstrate containing a polyimide compound; and chemically reacting saidpolymeric compound with said polyimide compound.
 2. The method of claim1, wherein said metal atoms of said metallacyclobutane group areselected from the group consisting of Si and Ge atoms.
 3. The method ofclaim 1, wherein said polymer has structural formula: ##STR18## whereinQ is selected from the group consisting of groups having structuralformula: ##STR19## ##STR20## where R is a divalent aromatic radicalwherein R¹ is selected from the group consisting of H, alkyl, aryl andalkenyl radicals;wherein R² is selected from the group consisting ofalkyl radicals, aryl radicals, alkenyl radicals and siloxy radicalshaving structural formula: ##STR21## wherein each R⁴ is selected fromthe group consisting of H, alkyl radicals, aryl radicals, alkenylradicals and silyl radicals having structural formula: ##STR22## whereineach R⁵ is selected from the group of H, alkyl, aryl and alkenylradicals; wherein R⁶ is selected from the group consisting of alkyl,aryl and alkenyl radicals; wherein R⁷ is selected from the groupconsisting of alkyl, aryl and alkenyl radicals; wherein R⁹ is selectedfrom the group consisting of alkyl, aryl and alkenyl radicals; whereinR¹⁰ is selected from the group consisting of alkenyl radicals; wherein Zis selected from the group consisting of aromatic radicals, wherein Zforms a six member carbon ring with the two carbon atoms to which it isbonded; wherein each M is selected from the group consisting of Si andGe atoms; wherein t has a value such that said compound has a molecularweight from about 1,000 to about 30,000; wherein m is at least 1; andwherein n is greater than or equal to
 0. 4. The method of claim 3,wherein the terminal R¹ O groups of said compound is replaced by groupshaving the structural formula: ##STR23## wherein R⁸ is an aryl group. 5.The method of claim 1, wherein said polymer is a reaction product ofp(bis-hydroxydimethylsilyl)benzene and at least one member selected fromthe group consisting of a1,1 -dichloro-1-silacylcobutane,1,3-dichloro-1,3-dimethyl-1,3-disilacyclobutane,1,1-dichloro-3,3-dimethyl-1,3-disilacyclobutane,1,1-dichloro-2,3-benzo-1-silacyclobutene,1,1-dichloro-3-methyl-1-silacyclobutene,1,1-dichloro-2-phenyl-1-silacyclobutane,1,1-dichloro-3,3-diphenyl-1,3-disilacyclobutane,1,1-dichloro-1-germacyclobutane and1,1-dichloro-3,3-dimethyl-1-sila-3-germacyclobutane.
 6. The method ofclaim 1 wherein said polymer is a reaction productofp(bis-hydroxydimethylsilyl)benzene, dimethyldichlorosilane and1,1-dichloro-1-silacyclobutane.
 7. The method of claim 1, wherein saidpolymer is a reaction product of p(bis-hydroxydimethylsilyl)benzene,dimethyldichlorosilane, dimethyldichlorosilane,1,1-dichloro-1-silacyclobutane and trimethylchlorosilane.
 8. The methodaccording to claim 1, wherein said thermal cross-linking is done withouta catalyst.
 9. The method of claim 1, wherein said cross-linking is at atemperature less than about 100° C. and wherein said metallacyclobutanegroup contains at least two metal atoms.
 10. A method according to claim1, wherein said polyimide substrate chemically reacts with saidpolymeric compound through an open imide ring on said polyimide compoundand said polymeric compound being grafted to a nitrogen atom in saidopen imide ring.